Multi-Band Equalizers

ABSTRACT

On-chip Multi-band equalizers for adjusting signal strength for a receiver receiving multi-band frequency signals are provided, The multi-band equalizer comprises multiple series connected tapped LC resonators. The tapped LC resonator may be capacitive tapping or inductive tapping, where both frequency and gain of the frequency bands of interest may be programmed by tuning the capacitances of the programmable capacitors and/or selecting the tapped out terminals of the inductors. The multi-band equalizer may be connected to a signal node, for instance between two amplifiers in the receiver.

TECHNICAL FIELD

Embodiments herein relate to multi-band equalizers. In particular, theyrelate to multi-band equalizers for adjusting signal strength for areceiver receiving multi-band frequency signals in a communicationdevice.

BACKGROUND

Wireless communication devices or equipment usually comprisetransceivers comprising transmitter and receiver. The transmittertypically up-converts baseband signals to Radio Frequency (RF) signalsfor transmission, and the receiver down-converts received RF signals tobaseband signals for further processing.

There is a trend towards very wideband implementations of receivers andtransmitters in wireless equipment like cellular base-stations. There isalso a trend towards more integrated solutions, i.e. to implement morefunctionality on-chip with integrated circuits. These trends aim atreducing the cost and increasing the flexibility of a solution. Awideband integrated receiver according to this trend will consist ofwideband amplifiers and an analog to digital converter (ADC). However,not all frequencies will be used for communication, and not all usedfrequency bands will arrive at the base-station with equal signalstrength. To address that, some off-chip components are used. These aremulti-band filters, such as triplexers, quadplexers, etc. The integratedcircuit can then feature individual variable gain amplifiers (VGAs) forthe different filter channels, which are then fed to a signal combiner.For high performance, a low noise amplifier (LNA) is used prior to themulti-band filter. The signal path thus enters the LNA chip at the LNAinput, exists the LNA chip to connect to the input of the multi-bandfilter, then again enters the VGA chip at the multiple VGA inputs. Ifthe signal combiner can then be implemented on-chip, the rest of thesignal path will be on-chip.

As can be seen the cost of equalizing the channel strengths is ratherhigh, with the signal path going off chip and then on-chip with multiplechannels, plus the cost of an off-chip customized multi-band filter. Alot of the flexibility of the solution is also lost due to themulti-band filter having fixed frequency bands. However, withoutequalizing the channel strengths, additional dynamic-range in the ADC isneeded, which would be very challenging to achieve and come at a highcost in power consumption. If different frequency bands are to be usedin the base-station, the multi-band filter needs to be replaced, and anew customized filter design is needed. Thus the multi-band filtersolution using an off-chip filter with fixed frequencies is in-flexible.Another major issue with this solution is noise, since when combiningthe output signals of the VGAs, their noise will also be combined. TheVGAs will produce noise at their outputs, which will be present not onlyat the frequencies of their own channels, but also at the otherchannels. The result of this is an increased effective receiver noisefigure due to the signal combination of the multi-band filterarchitecture.

SUMMARY

Embodiments herein provide an equalizer for adjusting signal strengthwith improved performance on flexibility, cost, size and/or noiseperformance.

According to one aspect of embodiments herein, there is provided amulti-band equalizer for adjusting signal strength for a receiverreceiving multi-band frequency signals. The multi-band equalizercomprises multiple resonators, each resonator has a first, a second anda third terminals. Each resonator comprises an inductor connectedbetween the first and second terminals and two programmable capacitorsconnected in series between the first terminal and second terminal. Theinterconnection of the two programmable capacitors is tapped out andconnected to the third terminal. The multiple resonators are seriesconnected such that the third terminal of a preceding resonator isconnected to the first terminal of a succeeding resonator. When used inthe receiver, the first terminal of the first resonator is connected toa signal node of the receiver and the third terminal of the lastresonator is connected to a signal ground, or the first terminal of thefirst resonator is connected to a signal ground and the third terminalof the last resonator is connected to a signal node of the receiver.

According to one aspect of embodiments herein, there is provided amulti-band equalizer for adjusting signal strength for a receiverreceiving multi-band frequency signals.

The multi-band equalizer comprises multiple resonators, each resonatorhas a first, a second and a third terminals. Each resonator comprises aninductor connected between the first and second terminals. The inductorhas two or more tapped out terminals with different inductances, the twoor more tapped out terminal are selectively connected to the thirdterminal. Each resonator further comprises a programmable capacitorconnected between the first and second terminals. The multipleresonators are series connected such that the third terminal of apreceding resonator is connected to the first terminal of a succeedingresonator. When used in the receiver, the first terminal of the firstresonator is connected to a signal node of the receiver and the thirdterminal of the last resonator is connected to a signal ground, or thefirst terminal of the first resonator is connected to a signal groundand the third terminal of the last resonator is connected to a signalnode of the receiver.

In other words, multi-band equalizers according embodiments hereincomprise multiple series connected inductor capacitor (LC) resonatorswith tapping. The number of simultaneous bands that can be supportedequals the number of LC resonators. The tapping may be either inductiveor capacitive and is programmable. Both center frequency and gain ofeach frequency band may be tuned by tuning the capacitances of theprogrammable capacitors and/or selecting the tapped out terminals of theinductors. By controlling the gain using programmable tapping the gaincan be changed without affecting the bandwidth of the resonators.

Multi-band equalizers according to embodiments herein may be included ina signal chain of wideband amplifiers, such as LNAs and VGAs, where asignal node between two amplifier stages is used to connect theequalizer. The first resonator may be connected to a signal node, andthe last to a signal ground. The signal node will then see an impedancethat is programmable, with peaks at the center frequencies of theresonators.

Multi-band equalizers according to some embodiments herein are flexible,since the frequencies of the bands may be changed by programming thecapacitances. By controlling the gain with tapping, rather than loading,the quality factor, i.e. the bandwidth of the resonators is independenton the gain setting.

Using a fully passive equalizer structure results in high dynamic rangeand low power consumption.

Multi-band equalizers according to embodiments herein are suitable foron-chip integration.

The number of simultaneous frequency bands may be scaled by includingmore resonators in the structure.

In some embodiments, a single amplifier chain may be used, and there isno need for parallel paths with noise issue related signal combination.

Therefore, embodiments herein provide multi-band equalizers withimproved performance on flexibility, cost, size and/or noise.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments herein are described in more detail withreference to attached drawings in which:

FIG. 1 is a schematic view of a multi-band equalizer according to afirst embodiment herein;

FIG. 2 is a schematic view of a multi-band equalizer according to asecond embodiment herein;

FIG. 3 is a schematic block view of a receiver front-end in which amulti-band equalizer according to embodiments herein is implemented;

FIG. 4 a) and b) are schematic views of differential multi-bandequalizers according to embodiments herein;

FIG. 5 shows simulation results for a multi-band equalizer withcapacitive tapping according to embodiments herein;

FIG. 6 shows simulation results for frequency tuning of a multi-bandequalizer with inductive tapping according to embodiments herein;

FIG. 7 shows simulation results for gain tuning of a multi-bandequalizer with inductive tapping according to embodiments herein;

FIG. 8 shows simulation results of gain, noise figure and input matchfor a receiver front-end with a multi-band equalizer according toembodiments herein;

FIG. 9 shows simulation results of the third order interception pointIIP3 and gain for a receiver front-end with a multi-band equalizeraccording to embodiments herein;

FIG. 10 shows an example inductor layout with taps according toembodiments herein; and

FIG. 11 is a block diagram illustrating a communication device in whicha multi-band equalizer according to embodiments herein may beimplemented.

DETAILED DESCRIPTION

FIG. 1 shows a multi-band equalizer 100 according to a first embodimentherein for adjusting signal strength for a receiver receiving multi-bandfrequency signals. The multi-band equalizer comprises multiple nresonators 101, 102, 103 . . . . Each resonator has a first 1, a second2 and a third 3 terminals. Each resonator comprises an inductor Ln,n=1,2,3 . . . connected between the first and second terminals, and twoprogrammable capacitors Cn1/Cn2, n=1,2,3 . . . , connected in seriesbetween the first terminal and second terminal. The interconnection ofthe two programmable capacitors is tapped out and connected to the thirdterminal.

The multiple resonators are series connected such that the thirdterminal of a preceding resonator is connected to the first terminal ofa succeeding resonator. For example, the third terminal of the firstresonator 101 is connected to the first terminal of the second resonator102, and so forth.

FIG. 2 shows a multi-band equalizer 200 according to a second embodimentherein for adjusting signal strength for a receiver receiving multi-bandfrequency signals.

The multi-band equalizer 200 comprises multiple n resonators 201, 202,203 . . . . Each resonator has a first 1, a second 2 and a third 3terminals. Each resonator comprises an inductor Ln, n=1,2,3 . . .connected between the first and second terminals, wherein the inductorhas two or more tapped out terminals with different inductances. The twoor more tapped out terminals are selectively connected to the thirdterminal.

Each resonator further comprises a programmable capacitor Cn, n=1,2,3 .. . connected between the first and second terminals.

The multiple resonators 201, 202, 203 are series connected such that thethird terminal of a preceding resonator is connected to the firstterminal of a succeeding resonator. For example, the third terminal ofthe first resonator 201 is connected to the first terminal of the secondresonator 202, and so forth.

When the multi-band equalizer 100, 200 is used in a receiver, the firstterminal of the first resonator may be connected to a signal node of thereceiver and the third terminal of the last resonator may be connectedto a signal ground, or other way around, the first terminal of the firstresonator may be connected to a signal ground and the third terminal ofthe last resonator may be connected to a signal node of the receiver.

The multi-band equalizer 100, 200 may be included in a signal chain ofwideband amplifiers, such as LNAs and VGAs, where a signal node betweentwo amplifier stages may be used to connect the equalizer. FIG. 3 showsan example receiver architecture where the multi-band equalizer 100, 200is used after VGA. The multi-band equalizer 100, 200 may be integratedon-chip together with other amplifier circuits LNA, VGA, AMP.

The tapped inductor structure may be used to feed bias current to thesignal node through the equalizer. This means that the equalizer may beused as a load to an amplifier stage.

The principle operation of the multi-band equalizer 100, 200 will beexplained in the following with reference to FIG. 1. As can be seen themulti-band equalizer 100 has 3 tapped resonators, each consisting of oneinductor Ln and two capacitors Cn1, Cn2. The parallel resonancefrequency, where the resonator has high impedance, is equal to

$\begin{matrix}{f_{{res},n} = \frac{1}{2\pi\sqrt{L_{n} \cdot \frac{C_{n\; 1} \cdot C_{n\; 2}}{C_{n\; 1} + C_{n\; 2}}}}} & (1)\end{matrix}$

The impedance of the resonator at resonance is equal to

R _(n)=2π·f _(res,n) ·L _(n) ·Q _(n)  (2)

Where Qn is the quality factor of the LC resonator. For on-chiprealizations this is typically in the order of 10, but there is atrade-off with chip area and tuning range.

The amount of this impedance seen at the equalizer input at theresonance frequency depends on the setting of the tap in the resonator,i.e. the ratio of Cn1 and Cn2. At that frequency the other resonatorsare off-resonance and their series connection will provide lowadditional impedance. So the total equalizer impedance in a certain bandwill be set by the resonator of that band and its tap setting. Atfrequencies far from resonance of any resonator, like between bands ofinterest, all series connected resonators provide low impedance. Thetotal impedance of the equalizer then gets low, the inter-bandinterferences signals are grounded through the equalizer, and the signallevels of inter-band interferences are then suppressed. Interference atsuch frequencies will then require less headroom in the ADC and causeless intermodulation distortion.

Therefore, according to the embodiments herein, a tunable multi-bandequalizer suitable for on-chip integration is realized. The multi-bandequalizer 100, 200 comprises multiple series connected tappedLC-resonators so that both center frequency and gain of each frequencyband may be tuned. Both the gain and resonance frequency are tunable bytuning the capacitances of the programmable capacitors in the multipleresonators. For each resonator, the gain and resonance frequency of thatresonator are tunable by tuning the capacitances of the programmablecapacitors and/or selecting the tapped out terminals of the inductor inthat resonator. The number of simultaneous bands that can be supportedequals the number of resonators. When the tunable multi-band equalizer100, 200 is connected to a signal node in a receiver, the signal nodewill then see an impedance that is programmable, with peaks at thecenter frequencies of the resonators, the magnitude of the peaks iscontrolled by the inductor tapping point selection or capacitance ratiosetting.

As shown in FIGS. 1 and 2, the tapping may be either inductive orcapacitive. In case of inductive tapping, each inductor has multipletaps which are selected by switches, and in case of capacitive tappingtwo series connected programmable capacitors are used in each resonator,with the tap in between.

With inductive tapping the resonance frequency is set using theprogrammable capacitor Cn, and the gain is set by programming theinductive tap. The tuning of frequency and gain are thus separated totwo different components so that the two parameters may then be tunedindependently. This provides for easier control of the circuit and lesstrade-offs due to conflicting simultaneous tuning ranges. A slightlymore complicated inductor layout will, however, result. However, sincethe highest quality factor is anyway typically not needed, this may berealized without significant compromises.

With capacitive tapping both the resonance frequency and gain are set bythe capacitors, so that when controlling the gain by changing the ratiobetween the capacitors Cn1, Cn2, the capacitance of the series connectedcapacitors must still be maintained not to alter the resonancefrequency, and vice versa. In this case there will be some limitationsin simultaneous tuning range of the two parameters that are not presentwith inductive tapping, but on the other hand the inductors have asimpler layout with capacitive tapping.

The multi-band equalizers 100, 200 shown in FIGS. 1 and 2 aresingle-ended. According to some embodiments herein, a differentialmulti-band equalizer may comprise two of the multi-band equalizers 100,200. FIG. 4 shows an example of a differential multi-band equalizercomprising two of the multi-band equalizers 100 with capacitive tapping,where a) shows a pseudo-differential multi-band equalizer 401 comprisingtwo single-ended equalizers, where inductors in two correspondingresonators are implemented separately, and b) shows a differentialmulti-band equalizer 402, where pairs of inductors in two correspondingresonators are implemented by transformers T1, T2, T3 to save chip area.Similarly, a differential multi-band equalizer may comprise two of themulti-band equalizers 200 with inductive tapping, where pairs ofinductors in two corresponding resonators may be implemented separatelyor by transformers.

To evaluate and demonstrate the performance of the multi-band equalizer100, 200, 401, 402, simulations are performed for a wideband receiver,e.g. 2 to 6.5GHz with 3 simultaneous bands. The simulations results ofthe multi-band equalizer 100 with capacitive tapping are shown in FIG.5, where the top figure shows tuning of the first frequency band e.g.2-3.2 GHz, the middle figure shows tuning of the second frequency bande.g. 3.5-5GHz, and the bottom figure shows tuning of the third frequencyband e.g. 5.4-7.5 GHz. As can be seen in the figures, the frequency andgain of each band may be configured without affecting the other bands.The frequency/amplitude controls are not orthogonal, but this is a minorissue that may be solved in the digital domain in a controller of theequalizer. There will, however, be a limitation in simultaneous tuningrange of frequency and gain.

The simulation results of the multi-band equalizer 200 with inductivetapping are shown in FIGS. 6 and 7, where FIG. 6 shows frequency tuningof each band, and FIG. 7 shows gain tuning of each band. As can be seenin the figures the frequency/amplitude of each band may be independentlycontrolled without affecting the other two bands. It is clear in thefigures that orthogonal frequency/amplitude configuration is inherentlyachieved.

Simulations have been performed on a receiver front-end with themulti-band tapped-inductor equalizer 200 added to it after a VGA, asshown in FIG. 3. To compare the performance the multi-band equalizer 200was disconnected and replaced with a 170 Ω resistor, approximately themaximum impedance of the equalizer at resonances. Simulation results ofthe receiver gain (top two curves), noise figure (NF) (middle curve) andinput match (S11) (bottom curve) are shown in FIG. 8. As can be seen inthe figure, the equalizer has negligible effect on NF and input matchwhile introducing three pass bands as desired.

The multi-band equalizer 100, 200, 401, 402 is implemented by passiveelements, including transistors operating as switches, and is thereforelinear. To investigate the linearity of a receiver chain including themulti-band equalizer, two-tone simulations have been performed with atone frequency spacing equal to 20 MHz. The frequency of the two tonesare swept across the desired RF frequency, e.g. from 2 to 6 GHz. Thesimulation result is shown in FIG. 9. The figure shows both the thirdorder interception point IIP3 and gain of the receiver front-end. As canbe clearly seen, the IIP3 is improved by the equalizer stop bandfiltering, i.e. the notch depth at different frequencies, e.g. at around2.8 GHz, 4.2 GHz.

Therefore, according to some embodiments herein, frequency notches ofthe multi-band equalizer 100, 200 may be controlled by tuning thecapacitances of the programmable capacitors and/or selecting the tappedout terminals of the inductors in the multiple resonators.

The implementation of the capacitive tapping or capacitive-divider basedequalizer is straight forward. It may be based on switched capacitors,where capacitors are switched in or out of the equalizer usingmetal-oxide-semiconductor (MOS) transistors. By programming thecapacitance values in this way, both the effective capacitance, whichsets the resonance frequency, and the capacitor ratio, which sets thegain, may be controlled. The tuning ranges of the capacitors are chosento cover both the frequency and gain range simultaneously, and asuitable number of bits in the digital control is then chosen to providethe resolution needed. The tapped inductor implementation, on the otherhand, needs to be more carefully designed for the required gain stepsand range. This is because the number of gain steps is directly relatedto the inductor layout, where many gain steps requires an inductor withmany taps. An example of a possible implementation of a taped inductoris shown in FIG. 10, where the inductor may be realized in the highestmetal layer and traces in the second highest layer may be used for thetaps. As can be seen there are 5 taps in this example.

To summarize, embodiments herein provide on-chip multi-band equalizersfor use in wideband receivers, where both frequency and gain of thefrequency bands of interest may be programmed. The multi-band equalizermay be connected to a signal node, for instance between two amplifierstages in the receiver. It then selects the bands of interest, and theirgain may be programmed without changing the bandwidth, using aprogrammable tapping of the resonators. By series connecting tappedLC-resonators no buffers are needed between stages, and the fullypassive structure of the multi-band equalizers provides high dynamicrange and extremely low power consumption. Using inductive tapping thegain and frequency may be controlled independently. The multi-bandequalizers according to embodiments herein reduce intermodulationdistortion due to interference, and reduce the dynamic range needed inthe ADC by equalizing the signal strengths of the signals of interest.Further, a single amplifier chain may be used, and there is no need forparallel paths with noise issue related signal combination.

The multi-band equalizers 100, 200, 401, 402 may be employed in variousintegrated circuits, electronic circuits or devices, communicationdevices or apparatus. FIG. 11 shows a block diagram for an electronicdevice 1100. The electronic device 1100 comprises a transceiver 1110which comprises a multi-band equalizer 100, 200, 401, 402. Theelectronic device 1100 may comprise other units, where a memory 1120, aprocessing unit 1130 are shown. The electronic device 1100 may be a userequipment or a mobile device, a wireless communication device, or aradio base station for a cellular communication system.

Those skilled in the art will understand that the multi-band equalizers100, 200, 401, 402 according to embodiments herein may be implemented byany semiconductor technology, e.g. Bi-polar, N-type Metal OxideSemiconductor (NMOS), P-type Metal Oxide Semiconductor (PMOS),Complementary Metal Oxide Semiconductor (CMOS), Fully Depleted Siliconon Insulator (FDSOI) or Micro-Electro-Mechanical Systems (MEMS)technology etc.

The word “comprise” or “comprising”, when used herein, shall beinterpreted as non-limiting, i.e. meaning “consist at least of”.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appended claims.

1-11. (canceled)
 12. A multi-band equalizer for adjusting signalstrength for a receiver receiving multi-band frequency signals, themulti-band equalizer comprising: multiple resonators, each resonatorhaving a first, second and third terminal, wherein each resonatorcomprises: an inductor connected between the first and second terminals;and two programmable capacitors connected in series between the firstterminal and second terminal, the interconnection of the twoprogrammable capacitors being tapped out and connected to the thirdterminal; and wherein the multiple resonators are series connected suchthat the third terminal of a preceding resonator is connected to thefirst terminal of a succeeding resonator and, when used in the receiver,the first terminal of the first resonator is connected to a signal nodeof the receiver and the third terminal of the last resonator isconnected to a signal ground, or the first terminal of the firstresonator is connected to a signal ground and the third terminal of thelast resonator is connected to a signal node of the receiver.
 13. Adifferential multi-band equalizer comprising two of the multi-bandequalizers of claim 12, wherein pairs of inductors in two correspondingresonators are implemented by transformers.
 14. A differentialmulti-band equalizer comprising two of the multi-band equalizers ofclaim
 12. 15. The multi-band equalizer of claim 12, wherein both gainand resonance frequency of the multiple resonators are tunable by tuningthe capacitances of the programmable capacitors in the multipleresonators.
 16. The multi-band equalizer of claim 12, wherein frequencynotches of the multi-band equalizer are controlled by tuning thecapacitances of the programmable capacitors and/or selecting the tappedout terminal of the inductor in the multiple resonators.
 17. Anelectronic device comprising a multi-band equalizer of claim
 12. 18. Theelectronic device of claim 21, wherein the electronic device is any oneof a receiver, a transmitter, a transceiver, a base station, a userequipment or a wireless communication device for a cellularcommunication system.
 19. A multi-band equalizer for adjusting signalstrength for a receiver receiving multi-band frequency signals, themulti-band equalizer comprising: multiple resonators, each resonatorhaving first, second and third terminals, wherein each resonatorcomprises: an inductor connected between the first and second terminals,wherein the inductor has two or more tapped out terminals with differentinductances, the two or more tapped out terminals being selectivelyconnected to the third terminal; a programmable capacitor connectedbetween the first and second terminals; and wherein the multipleresonators are series connected such that the third terminal of apreceding resonator is connected to the first terminal of a succeedingresonator and, when used in the receiver, the first terminal of thefirst resonator is connected to a signal node of the receiver and thethird terminal of the last resonator is connected to a signal ground, orthe first terminal of the first resonator is connected to a signalground and the third terminal of the last resonator is connected to asignal node of the receiver.
 20. A differential multi-band equalizercomprising two of the multi-band equalizers of claim
 19. 21. Adifferential multi-band equalizer comprising two of the multi-bandequalizers of claim 19, wherein pairs of inductors in two correspondingresonators are implemented by transformers.
 22. The multi-band equalizerof claim 19, wherein, for each resonator, the gain and resonancefrequency of that resonator are tunable by tuning the capacitance of theprogrammable capacitor and/or selecting the tapped out terminals of theinductors in that resonator.
 23. The multi-band equalizer of claim 19,wherein frequency notches of the multi-band equalizer are controlled bytuning the capacitances of the programmable capacitors and/or selectingthe tapped out terminal of the inductor in the multiple resonators. 24.An electronic device comprising a multi-band equalizer of claim
 19. 25.The electronic device of claim 24, wherein the electronic device is anyone of a receiver, a transmitter, a transceiver, a base station, a userequipment or a wireless communication device for a cellularcommunication system.